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Old 15th October 2014, 11:59   #376
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

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Originally Posted by mayankk View Post
By engine load, did you mean the fuel consumption, then?
Engine Load is one of the PIDs being exposed by the Duster ECU

Last edited by ::CMS:: : 15th October 2014 at 12:15.
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Old 15th October 2014, 18:48   #377
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

Assuming that fuel consumption in a proper gear without clutching is lesser than in neutral/idling could only be an assumption?

If the idling rpm is say, 1200 and rpm in proper gear is, say 1800; when running in gear the engine has to run 600 rpm more. Engines are tuned to consume to barely avoid stalling in gear or in neutral. In gear, without throttle DFCO comes in, so no fuel consumed, but engine is spun at 1800 still and eats up the momentum. Eventually we need to throttle up for additional rpms.

In gear state consuming less fuel would be possible only when energy needed to keep an engine at idle rpm than a (much) higher rpm.

That said, the question on whether being in neutral and saving whatever amount of fuel is worth it, is a totally different question altogether!

PS: Engine gurus can comment please, somewhere I remember reading most significant efficiency losses come from keeping the engine running or the internal losses.
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Old 16th October 2014, 16:39   #378
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

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Originally Posted by babu.sundaram View Post
Assuming that fuel consumption in a proper gear without clutching is lesser than in neutral/idling could only be an assumption?

If the idling rpm is say, 1200 and rpm in proper gear is, say 1800; when running in gear the engine has to run 600 rpm more. Engines are tuned to consume to barely avoid stalling in gear or in neutral. In gear, without throttle DFCO comes in, so no fuel consumed, but engine is spun at 1800 still and eats up the momentum. Eventually we need to throttle up for additional rpms.

In gear state consuming less fuel would be possible only when energy needed to keep an engine at idle rpm than a (much) higher rpm.

That said, the question on whether being in neutral and saving whatever amount of fuel is worth it, is a totally different question altogether!

PS: Engine gurus can comment please, somewhere I remember reading most significant efficiency losses come from keeping the engine running or the internal losses.
I think this was discussed several times in the past. The rpm doesnt say anything about the fuel consumption as both fuel and the momentum of the flywheel can run the engine. While idling, the fuel is pumped to keep a particular rpm say 800 and the same is not required when the engine uses the flywheel to keep the same rpm ie, less fuel is consumed till it reaches the idle rpm where the anti-stall kicks in.

Engine load somewhat says the status of the engine at a particular point of time, I have observed, while moving at say 60km/hr, on neutral the load stays around 50% and at the same time costing in the proper gear makes the engine load ~25-30%, the moment you put the gear to neutral the load goes upto ~50%. The same happens when you lug the engine, it goes to ~80-90%, hence we say more fuel is consumed if you lug the engine or if not in proper gear based on the rpm.

Last edited by ::CMS:: : 16th October 2014 at 16:41.
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Old 16th October 2014, 19:47   #379
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

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Originally Posted by ::CMS:: View Post
I think this was discussed several times in the past. The rpm doesnt say anything about the fuel consumption as both fuel and the momentum of the flywheel can run the engine. While idling, the fuel is pumped to keep a particular rpm say 800 and the same is not required when the engine uses the flywheel to keep the same rpm ie, less fuel is consumed till it reaches the idle rpm where the anti-stall kicks in.

Engine load somewhat says the status of the engine at a particular point of time, I have observed, while moving at say 60km/hr, on neutral the load stays around 50% and at the same time costing in the proper gear makes the engine load ~25-30%, the moment you put the gear to neutral the load goes upto ~50%. The same happens when you lug the engine, it goes to ~80-90%, hence we say more fuel is consumed if you lug the engine or if not in proper gear based on the rpm.
On contrary, just think in plain physics. It needs energy to turn the engine. More energy is needed when you turn it faster. Idle rpm is lower than the in-gear rpm. So, more energy is needed when engine is in-gear.

Given that fuel is the only source of energy (no regenerative mechanism kicking in like braking situations) in-gear must consume more fuel. Isn't it?

(Momentary readings could be misleading as there would be variations due to flywheel, slope up/down, etc).

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Originally Posted by Samurai View Post
Actually, it depends on the load on the engine.
Energy needed would be same, where the energy comes from (fuel/flywheel) depends on the load.

Last edited by babu.sundaram : 16th October 2014 at 20:11. Reason: Edited to respond to next post.
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Old 16th October 2014, 20:00   #380
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

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Originally Posted by babu.sundaram View Post
On contrary, just think in plain physics. It needs energy to turn the engine. More energy is needed when you turn it faster. Idle rpm is lower than the in-gear rpm. So, more energy is needed when engine is in-gear.
Actually, it depends on the load on the engine.
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Old 16th October 2014, 22:12   #381
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Quote:
Originally Posted by babu.sundaram View Post

On contrary, just think in plain physics. It needs energy to turn the engine. More energy is needed when you turn it faster. Idle rpm is lower than the in-gear rpm. So, more energy is needed when engine is in-gear.
That energy is being provided by the wheels turning the engine over, not fuel. The rpms could be 3000 but fuel going in would be zero, less than what is pumped in neutral/idle.
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Old 17th October 2014, 14:22   #382
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

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Originally Posted by mayankk View Post
That energy is being provided by the wheels turning the engine over, not fuel. The rpms could be 3000 but fuel going in would be zero, less than what is pumped in neutral/idle.
The energy to turn wheels also comes from fuel.

Eventually, the additional energy needed to turn engine at a higher speed has to come from only fuel tank (as there are no other energy sources!), though momentarily it could come from vehicle's momentum (or from the incline if vehicle is going down).

Neutral with no throttle input would be the lowest fuel consumption case, except when engine braking is used (where vehicle's momentum is used up to turn the engine).
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Old 17th October 2014, 14:42   #383
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

[quote=babu.sundaram;3558752]Neutral with no throttle input would be the lowest fuel consumption case, except when engine braking is used (where vehicle's momentum is used up to turn the engine).

Sorry, LOL.

Atleast try to understand how a modern engine and ECU works before making vague statements like this. For proper engine braking, you may need to throttle to match the rpm with gear, otherwise your transmission can conk off or too much stressed. If you meant coasting in gear, then its the best to save fuel and maintain the desired speed, period.

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Old 17th October 2014, 15:06   #384
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

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Originally Posted by ::CMS:: View Post
While idling, the fuel is pumped to keep a particular rpm say 800 and the same is not required when the engine uses the flywheel to keep the same rpm ie, less fuel is consumed till it reaches the idle rpm where the anti-stall kicks in.
So far correct.

Let me just put "Load" into simple terms. It is the amount of fuel required to turn the engine at a given RPM.

A car with just me at 1500 rpm and 50kmph will be using much less fuel (hence much less load on the engine) than when the car is doing the same 1500 RPM and 50kmph with 5 People (more fuel required = More load on engine).

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Originally Posted by ::CMS:: View Post
I have observed, while moving at say 60km/hr, on neutral the load stays around 50% and at the same time costing in the proper gear makes the engine load ~25-30%, the moment you put the gear to neutral the load goes upto ~50%. The same happens when you lug the engine, it goes to ~80-90%, hence we say more fuel is consumed if you lug the engine or if not in proper gear based on the rpm.
One small thing. Here by coasting you obviously mean Throttle closed and not maintaining 60kmph.

That means you are deceleration from 60kmph in gear. Therefore engine is getting a part of or entire energy from the momentum of the car (Hence slowing down - apart from road, air resistance etc). Hence the lower load percentage shown compared to neutral.

Quote:
Originally Posted by babu.sundaram View Post
On contrary, just think in plain physics. It needs energy to turn the engine. More energy is needed when you turn it faster. Idle rpm is lower than the in-gear rpm. So, more energy is needed when engine is in-gear.
Yes, but when coasting (0 throttle) in gear, the wheels are driving the engine. Therefore no/less fuel is injected to turn the engine over.

But when in neutral, only fuel is responsible for turning the engine over albeit at the idle rpm. Only fuel is responsible for overcoming the inertia, friction or all the running parts of the engine.


Quote:
Originally Posted by babu.sundaram View Post
Given that fuel is the only source of energy (no regenerative mechanism kicking in like braking situations) in-gear must consume more fuel. Isn't it?
Again depends on what situation you are talking about. If you are coasting (0 throttle) you are invariably decelerating. Hence engine breaking or regeneration occurs.

If you are talking about maintaining a given speed, this conversation is moot.

Simple physics,
Neutral - no energy to wheels - so no maintaining of speed - fuel burnt at idle speed.
Part throttle to maintain speed - energy to wheels from fuel burnt - speed maintained.

So for a given distance to be covered in given time, Part throttle speed maintenance is more fuel efficient than "in-neutral-speed-loss and more-throttle-speed-gain" cycles.

Quote:
Originally Posted by babu.sundaram View Post
Neutral with no throttle input would be the lowest fuel consumption case, except when engine braking is used (where vehicle's momentum is used up to turn the engine).
Yes, but to what end. You will be going nowhere. Its the lowest fuel consumption when your motive is to simply turn over the engine.

To get from A to B in a given time, there are two ways (idealized).

Accelerate to the required average speed and maintain in gear.

Accelerate to a much higher speed and at a calculated time, shift to neutral and let the momentum get you to B.

I think it is obvious that the first case will be more efficient in real world terms when resistances are taken into account which increase non linearly with speed. And in the second case, you will be running the engine on idle with absolutely no contribution to your motive of reaching the destination. Plus the fact that we need to slow down regularly makes the case for engine braking - more fuel efficient technique.


Last edited by rangakishen : 17th October 2014 at 15:07.
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Old 18th October 2014, 06:37   #385
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

This is an odd query in my thought process.

One brakes to slow down, but typically one either shifts down a gear or two either just before braking or simultaneously during braking.

One rarely jams the brakes and keeps one's foot on them for prolonged periods, unless one is in an automatic transmission vehicle.

This concept of shifting to neutral while braking is alien to me unless one has come to an absolute dead halt and switched the car off, with the handbrake on.

Pressing the clutch while braking is done only for the reasons stated earlier above.

Especially if one drives in a hilly area, one very quickly realises the value of smart, anticipatory and quick gear changes, in order to take full advantage of the "engine braking" effect irrespective of whether one is travelling uphill or downhill, the same principle applies.

In my humble opinion/ submission, it would be downright silly to shift to neutral while braking when one is driving thus, in the hills or indeed, anywhere else even, on the public roads.
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Old 21st October 2014, 11:24   #386
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

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Originally Posted by shankar.balan View Post
This is an odd query in my thought process.

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.
.
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This concept of shifting to neutral while braking is alien to me unless one has come to an absolute dead halt and switched the car off, with the handbrake on.

Pressing the clutch while braking is done only for the reasons stated earlier above.

Especially if one drives in a hilly area, one very quickly realises the value of smart, anticipatory and quick gear changes, in order to take full advantage of the "engine braking" effect irrespective of whether one is travelling uphill or downhill, the same principle applies.

In my humble opinion/ submission, it would be downright silly to shift to neutral while braking when one is driving thus, in the hills or indeed, anywhere else even, on the public roads.

When you want to stop, it is best to use all the available resources - brakes and engine, no point in shifting to neutral before stopping.

In fact just to keep in practice, I regularly (when the circumstances permit) down shift sequentially from 4th to 1st for stopping. This gives me an idea of how fast I can stop without brakes, so that I am not flummoxed in an emergency. I also rarely brake when there is plenty of time to downshift and slow down. I general I subscribe to my driving instructors advice - in general, drive the car as though you are driving a Limo, no jerks either while accelerating or while slowing down. That does not mean that I have no fun. When I am in a mood and the roads permit, I shift gears at 5500 RPM while accelerating and for aggressive breaking down shift similarly while braking.
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Old 21st October 2014, 12:29   #387
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

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Originally Posted by Aroy View Post

When you want to stop, it is best to use all the available resources - brakes and engine, no point in shifting to neutral before stopping.
While shifting into neutral is something I never do unless I have stopped completely, I do make use of clutch while braking. The sequence of situations is something like this:

Slowing down a bit: Just take off your foot from the accelerator.

Slowing down a bit more but the need to downshift is not anticipated: Just use brake without touching the clutch.

Downshift is anticipated start pressing clutch along with the brake. Downshift when required to appropriate gear depending on speed.

In such situations I have begun pressing the clutch along with the brake. So if I have to slow down from 60 to 30, by the time reach 40 my clutch is pressed and either I change the gear or just slowly lift off my foot if the change is not required.

In other words I do not rely predominantly on engine braking. It seems to me to have served me well till now.
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Old 21st October 2014, 13:03   #388
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Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

If you use engine braking, it could stop before the point you want to stop. But putting neutral could take you far enough. One can judge the distance and determine this.

Although I dont use neutral before coming to stop like in a traffic light, cant say that using engine braking with lesser fuel used would always benefit.

But you should coast in gear by judging the distance to stop.
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Old 26th October 2014, 15:59   #389
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Originally Posted by racer_m View Post
I have the complete opposite view.

1. You are not in control of the car. Remember in a braking situation you definitely need the so called "annoying braking effect". In a panic braking situation, the less said about being is neutral the better.
To be honest, I'm still not convinced with the reasons...

If the brakes or the steering wheel does not work, then you maybe out of control... When you shift to neutral, YOU ARE IN CONTROL OF THE CAR. Just because momentum takes over, and you feel that extra lunge, to say that you are not in control is just a perception... it will take a little getting used to...

Also, when you are > 3rd gear, I don't think the braking effect of the engine is going to help a lot in a panic braking situation... maybe < 3rd gear it may help a little bit...


Quote:
Originally Posted by racer_m View Post
2. You will seriously wear out your clutch/gear/drive train mechanism just to save some imaginary fuel. Seriously you strain a lot of components when you suddenly slot in a gear right from neutral at a high speed.
Here I partially agree with you ... If there is a huge difference in RPM, then there would be more strain, so more or less matching the RPM while shifting back into gear is important... this comes with practice...

Quote:
Originally Posted by racer_m View Post
3. You will wear out your whole body rather than just one leg, by doing the gear shift/clutch/steering circus for the neutral coasting (and that too very frequently)

4. You will be more distracted/exhausted and juggle your concentration between Speedometer/Road Hazards/Correct shifting, etc rather than focus on a relaxed driving and observing the environment around you.
I actually find this very relaxing thing to do... initially, if you are used to driving in gear, you may find this a little hard getting used to... but once you understand how to use momentum, you'll also find it easy to drive like this

I get distracted/irritated when someone else drives and does not make use of momentum... unnecessarily maintaining the engine RPM at higher levels


So IMO, i think that "Don't drive in neutral, always drive in gear" is just a traditional perception... I think we should make use of the momentum instead of wasting it (down hill is an exception)...
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Old 26th October 2014, 16:48   #390
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Originally Posted by AjayJoshuaN View Post
To be honest, I'm still not convinced with the reasons...



So IMO, i think that "Don't drive in neutral, always drive in gear" is just a traditional perception... I think we should make use of the momentum instead of wasting it (down hill is an exception)...

Feel free, but in most western countries you would flunk the driving test if you exhibit this behavior.

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